The light-emitting diode (LED) emits light by transforming the energy released from the electrons moving between the n-type semiconductor and the p-type semiconductor so the mechanism is different from that of the incandescent lamp. Thus, the LED is called cold light source. In addition, because the LED has advantages like high reliability, long lifetime, compact size, low power consumption, and so on, the current illumination market expects the LED to be an illuminant tool of the new generation.
The conventional LED structure is a semiconductor epitaxial structure formed on a substrate, wherein the quality of the epitaxy in the semiconductor epitaxial structure has critical influence on the internal quantum efficiency of the LED, and whether the lattice constant of the substrate can match with that of the material of the epitaxial structure is important to the quality of the epitaxy. Therefore, the choice of the substrate materials for the LED is limited.
In addition, to improve the light extraction efficiency and heat-dissipation of the LED, the technique of transferring the substrate of the LED comes up gradually. Referring to FIG. 1A to FIG. 1G, a flowchart for a conventional substrate transfer process is illustrated. As shown in FIG. 1A, a first substrate 10 is provided, and an epitaxial structure 12 is provided as shown in FIG. 1B. Referring to FIG. 1C, then a second substrate 14 is provided, and an adhesive layer 16 is, referring to FIG. 1D, formed on the second substrate 14. Later, referring to FIG. 1E, the structure illustrated in FIG. 1A is flipped to attach the epitaxial structure 12 with the second substrate 14 with the adhesive layer 16 by pressed lamination, wherein the material of the adhesive layer 16 can be metal or polymers like PI, BCB, PFCB, and combinations thereof. After that, referring to FIG. 1F, the substrate 10 is removed so as to form a conventional light-emitting diode structure illustrated in FIG. 1G.